Forgive the "Master of the Obvious" comment, but the stripeless jerseys are obviously their warm-weather jerseys. The Saints game in question was played on a warm (high of 82) day in New Orleans, and below is a sideline shot from the 12/7/69 Vikings game that was played in Los Angeles:

Yes, that's what I was thinking, too. The Lions' jersey to which I alluded was worn in the '68 season opener, in the Cotton Bowl. It suggests that this was the year the NFL realized that, on an 80-degree day, the players could do without the sleeves which went halfway down the forearm.

I thnk Bill will confirm this, but we sorta had this pegged for 1968, but we weren't sure if the Vikies did indeed go stripeless, I just couldn't get a good pic/film from that MIN-NO to fully confirm. Tommy F's screen shots did just that and we thank him for the assistance.

So, the Vikes went from 1968 thru 1973 where they wore both the mesh-stripeless purples and the striped-durenes.

The dual mesh/durene styles seemed to end in 1973 as I would guess most of the jersey makers were finally able to conquer the problem of properly stitching/screening issues by 1974. Only a couple of rare instances extend from 1974 with striping issues, notably the Eagles, but that had to do with them using the wire mesh and the standard mesh jerseys.